Loudspeaker voice coils

ABSTRACT

An improvement in the method and manner of constructing a loud speaker voice coil, such improvement consisting of utilizing conductive metal foil as the wound element for supported positioning and reciprocal movement within an associated magnetic air gap; such a metallic foil coil may consist of one or more turns of either superimposed or alternately off-set foil windings.

United States Patent 1 Bremseth LOUDSPEAKER VOICE COILS [76] Inventor:Gerald B. Brernseth, 5700 NW.

67th St., Oklahoma City, Okla. 73|32 Filed: Jan. 20, 1971 Appl. No.:107,994

US. Cl. ..l79/ll5.5 VC, 336/223 Int. Cl. ..I-I04r 9/04 Field ofSearch.....l79/I-l5.5 R, 115.5 DV, I 15.5

[56] References Cited UNITED STATES PATENTS 2,445,276 Massa .1 ..l79/l15.5 vc

[4 1 Jan. 16, 1973 FOREIGN PATENTS OR APPLICATIONS 383,664 ll/l932 GreatBritain ..I79/l 15.5 VC

Primary Examiner-Kathleen H. Claffy Assistant Examiner-Douglas W. OlmsAttorney-Dunlap, Laney, Hessin & Dougherty [57] ABSTRACT An improvementin the method and manner of con structing a loud speaker voice coil,such improvement consisting of utilizing conductive metal foil as thewound element for supported positioning and reciprocal movement withinan associated magnetic air gap; such a metallic foil coil may consist ofone or more turns of either superimposed or alternately off-set foilwindings.

2 Claims, 5 Drawing Figures volume-efficiency.

BACKGROUND OF THE INVENTION 1. Field of the Invention v The inventionrelates generally to the art of audible sound reproduction and, moreparticularly, but not by way of limitation, it relates to improved voicecoil apparatus for use in loudspeaker assemblies.

2. Description of the Prior Art The prior art includes no teaching as toa similar type of voice coil structure as formed by wound metallic foil.The use of foil has been known in constructing certain transformer andradio frequency coil structures, and particularly in such applicationswherein the inherent characteristics and structural capabilities of foillend themselves to particular applications. There are no known teachingsheretofore which extend in any way into the sound reproduction art.

SUMMARY OF THE INVENTION The present invention contemplates an improvedtransducer drive coil wherein the drive coil assembly is constructed ofone or more windings of a metallic foil of selected thickness and width.The wound foil coil may be varied in any of foil thickness, foil width,type and configuration of foil overlap per winding, etc., to varyaccordingly the inductance characteristics of the coil for particularapplications.

Therefore, it is an object of the present invention to provide animproved acoustic energy transducer drive coil which offers theadvantages of increased strength, simplicity, heat-dissipationcapability, and high It is also an object of the invention to provide atransducer drive coil having higher power handling capability per unitsize of structure.

It is still further an object of the present invention to provide aloudspeaker voice coil of high efficiency which can be constructed withdecreased thickness and volume as compared to prior art forms of voicecoil.

Finally, it is an object of the present invention to provide aloudspeaker or microphone voice coil which is inherently stronger thanlike units formed with prior construction techniques and materials, andwhich foil voice coil exhibits increased exposure surface while allowingless dead space within the magnetic gap volume.

Other objects and advantages of the invention will be evident from thefollowing detailed description when read in conjunction with theaccompanying drawing which illustrates the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a vertical section through aloudspeaker structure which utilizes a voice coil constructed inaccordance with the present invention;

FIG. 2 is a side elevation of a coil former and voice coil constructedin accordance with the invention;

FIG. 3 is a partial vertical section showing one form of coil former andvoice coil relationship; 7

FIG. 4 is a partial vertical section showing an alternative form of coilformer and and I FIG. 5 is a vertical section'through a typical form ofdome diaphragm utilizing a foil coil constructed in accordance with theinvention.

voice coil configuration;

DETAILED DESCRIPTION OF THE INVENTION While the teachings of theinvention are applicable to any of various types of electromagnetictransducing assembly, the description proceeds relative to an exemplaryapplication in an acoustic energy generating device. Thus, referring nowto FIG. 1, a conventional form of loudspeaker assembly 10 consists of aframe element 12 supporting a diaphragm l4 and driver assembly 16. Theframe element 12 consists of an outer ring frame 18 and such as aclamping ring 20 suitably fastened therebeneath to receive and hold anouter peripheral edge 22 of diaphragm 14. Diaphragm 14 is of the usualconstruction having such as molded concentric ridges 24 adjacent theouter supporting point or peripheral edge 22.

An inner circumferal edge 26 of diaphragm 14 is formed as a cylindricalsleeve and secured as by bonding with suitable epoxy or the like to theoutside of one end of a coil former 28, i.e., usually a cylindrical tubesection formed of phenolic plastic or the like and secured to diaphragm14 in axial alignment therewith. Centering of the diaphragm l4 and coilformer 28 is effected in usual manner by a resilient spider 30 which issuitable bonded at the point of juncture of diaphragm l4 and coil former28 to extend radially outward for circumferal affixure to the speakerframe, shown schematically as dash-line 32. Thus, the frame portion 32provides secure structure from the outer frame ring 18 rearward tosupport and align the various operating elements of the loudspeaker 10,this structure being wellknown and conventional in design.

The magnet assembly 16 is rigidly supported by frame portion 32 so thatit is maintained in magnetically interactive relationship with coilformer 28 and voice coil 34. The voice coil 34 is comprised of one ormore turns of a selected foil material as wound circuitously around thelower end 36 of coil former 28 to be moveably supported within asymmetrically shaped air gap 38 as formed by magnet assembly 16. Thevoice coil 34 may be wound from any of selected metallic foil materials;however, operation has been achieved to excellent advantage usingaluminum foil of thickness 0.001 inch. Any of various metal foils oralloy foils may be used. The thickness too is a matter of choicedepending upon the type of speaker performance and the characteristicsto be stressed.

The magnetic assembly 16 is of conventional design having a cylindricalmagnet 40 and a center pole portion 41, and an annular ring portion42'is secured by a brace portion 44 to maintain the proper circular airgap 38. The type and configuration of magnetic assembly I6 may also bevaried so long as a sufficient size of air gap 38 is provided to receivethe voice coil 34.

FIG. 2 illustrates the manner in which voice coil 34 is connected torespective take-down leads 46 and 48, shown in FIG. I as connectedthrough diaphragm 14 to signal supply leads 50. As can be noted in FIG.2, the wound foil voice coil enables a further advantage of utilizingfolded extensions of the coil foil as the take down leads 46 and 48.This is proven to be a superior method of take-down lead constructiondue to the fact that the foil is extremely thin and can be folded atright angles and led out of the coil configuration without the need fora special tolerance in the magnetic structure.

Thus, a speaker with a foil coil need not suffer an efficiency loss dueto the necessity to provide a clearance for the take-down lead as hasbeen a chronic problem in conventional loudspeaker designs of singlelayer coil construction. Each of the take-down leads 46 and 48 is madeby folding a simple 90 bend in the foil ends so that the ends (leads 46and 48) extend along the coil former 28 for suitable connection to theexternal energizing voltage input. Such energizing voltage may beapplied by any of various well-known connection methods; however, asshown in FIG. l,'connection may be by suitable solder joint or otheraffixure through the diaphragm 14 to voltage supply leads 50.

The foil coil winding may be arranged in any of various cross-sectionalconfigurations. Thus, as shown in FIG. 3, the foil coil 34 is woundabout the lower end of coil former 28 which each successive foil overlayplaced in exact superposition over prior wrapped layers. The coil 34 mayconsist of as many overlays 54 as are needed in establishing therequisite inductive characteristics; and also, the choice of foil width,thickness, metal type, etc. are subject to similar selection andadjustment.

FIG. 4 illustrates an alternative form of foil coil 56 which is woundwith alternate foil overlays 58 off-set by a pre-determined distancedenoted by arrows 60, such configuration enabling much increasedexternal exposure surface to each individual foil overlay 58. Thus, incertain applications where dead space may not be critical, and heatdissipation may become a primary consideration, the cross-sectionalconfiguration such as that of foil coil 56 may be desirable. It shouldbe understood that various cross-sectional configurations and foiloverlay patterns different from those shown may find use in certainspecial applications. It is also contemplated that it may beadvantageous to vary the foil thickness or width along its length tofurther alter the concentration of inductive material about the coil.

In operation, the speaker assembly functions in generally the samemanner utilizing foil coil 34 as does the conventional speaker assemblyutilizing a wound wire coil. The only differences in operation are inthe improvements of certain physical characteristics as enabled by thefoil coil. Thus, the foil voice coil has served to overcome somepersistent problems in speaker manufacture such as coil concentricity.This is an especial problem with construction of the larger voice coilsizes, and coils formed in accordance with the foil coil method haveproven to be much more resistant to warping than are conventional wirewound coils. In the usual practice, the curing of a very thin epoxybonding agent in and around the combination of many layers of thin foilforms a monolithic block which is inherently stronger than conventionalvoice coil structures. Another common failing of conventional voicecoils is the loosening of the end turns of the coil in response tocertain stress movements, which loosening quickly weakens and lessensdependability of the coil structure. In the case of the foil coil thereare no end turns to loosen as the entire surface of each foil layer isfirmly bonded or attached to the next foil layer above (as wellas'below) with the result that the entire coil package is extremelysturdy and exhibiting a high affinity for coil concentricity. I

The method of foil coil construction also has an increased advantage insimplicity. Thus, acoil winding machine needs no complex traversemechanism, no gears, no cams, etc. The coil is easily positionedaccurately on the-coil former, and thereafter it is easily inspected andhandled in further assembly. In construc; tion, the designer has theadvantage of knowing the precise measurement of the axial length of thecoil since this is the width of the foil itself. There are so manyvariables in normal wire coil construction practice that it has beenusual to design the speaker to operate with a rather large tolerance inthe axial length of the voice coil. This practice then contributesto awasting or a failure to utilize all or an appreciable majority of theavailable magnetic flux across the associated air gap.

FIG. 5 illustrates a foil coil as constructed in accordance with theinvention and utilized in a highpowered compression driver hornapplication. Thus, FIG. 5 illustrates a dome diaphragm 70,-as iscommonly utilized in a driver unit of a horn assembly. The domediaphragm consists of a dome portion 72 and cylindrical side wall 74which is formed integrally with a radially extending spider portion 76to be suitably retained in annular clamping assemblies 78 and 80, as iswell-known. A coil former 82 of cylindrical form is axially aligned withthe cylindrical side wall 74 of diaphragm 70 and securely affixedthereto by suitable bonding, e.g., by epoxy cement or the like. A foilcoil 84 is then wound around the lower end of coil former 82, such foilcoil 84 being suitably bonded in the manner as previously set forth. Thetake-down leads from foil coil 84 may be led out in any of various ways;however, it may prove advantageous in many applications to lead the foilstrip take-down leads 86 (shown in dash-lines) outward along the underside of spider portion 76 of dome diaphragm 70. Such practice willresult in no unnecessary drag or unbalancing of the spider element tohamper operation of the driver assembly. lt is also foreseen that someapplications will allow elimination of the coil former memberaltogether.

The foregoing describes a novel voice coil which has many inherentadvantages. The invention is superior to all other types of voice coilconstruction in its ability to dissipate heat. Thus, a multi-layer foilvoice coil may be made such that each turn has two edges exposed forheat dissipation. The fact that there are no trapped turns, as are foundin conventional square or round wire coils, also allows the coil to heatevenly with no hot spots. This enables the voice coil to make maximumuse of the available magnetic flux within the air gap of the magnetassembly, there being no dead air space. The ability to increase thecross-sectional area of the conductor within the flux gap serves toincrease the volume-efficiency of the voice coil. That is, theefficiency ofa loud speaker varies as the square of the magnetic fluxdensity times the square of the length of wire within the air gap. Sincethe length of wire with a given cross-sectional area and a givenresistance is fixed, and the magnetic flux density increases withreduction of the magnetic gap volume, the volume-efficiency of the coilwill be the controlling factor in the ef ficiency of a speaker with agiven magnet structure.

The use of the foil coil and advanced insulation and bonding measures ofan extremely thin coating contribute to the lessening of the dead spacein the center of the magnetic gap and therefore, this effects anincrease in the volume-efficiency of the coil. Such increase enables thebest use of the magnetic flux available in the given magnetic gapthereby to convert more of the electrical energy to acoustic energy thanwould be possible with a conventional speaker utilizing a wire woundvoice coil. This, in turn, will result in less of the electrical energybeing converted to heat, and the combination of the features brings intobeing the possibility of construction of loud speakers with higherefficiency and higher power-handling capability than any yet designed.

It should be understood too that the employ of single and multi-layerfoil coil energizing units is by no means limited to loudspeakerassemblies. Various other forms of electromagnetic transducer, such asthe numerous types of microphone and many accelerometer devicesincluding high-powered shake table transducers, should gain functionaladvantage with utilization of the foil coil teachings.

Changes may be made in the combination and arrangement of elements asheretofore set forth in the specification and shown in the drawing; itbeing understood that changes may be made in the embodiments disclosedwithout departing from the spirit and scope of the invention as definedin the following claims.

What is claimed is: l. in an electromagnetic transducer assembly of thetype having a frame member supporting a diaphragm in contact with thesurrounding air, and a magnet assembly secured in place by said framemember to define an air gap having magnetic flux present thereaeross,the coil structure comprising:

coil former means securely affixed to said diaphragm and disposed to besupported within said air gap;

coil means formed from metallic foil wound in circuitous form, said coilmeans being wound upon said coil former means within said air gap witheach alternate winding of said metallic foil in an off-set relationshiprelative to a mid-position within said air gap;

means providing insulation between any one part of said metallic foiland another part of said metallic foil; and

conduction means providing electrical connection to each one of theopposite ends of said metallic foil.

2. A transducer assembly as set forth in claim 1 wherein said strip ofmetallic foil is formed into a coil with successive windings displacedfrom superposition by predetermined amounts which vary the inductivecharacteristics in pre-set manner,

1. In an electromagnetic transducer assembly of the type having a framemember supporting a diaphragm in contact with the surrounding air, and amagnet assembly secured in place by said frame member to define an airgap having magnetic flux present thereacross, the coil structurecomprising: coil former means securely affixed to said diaphragm anddisposed to be supported within said air gap; coil means formed frommetallic foil wound in circuitous form, said coil means being wound uponsaid coil former means within said air gap with each alternate windingof said metallic foil in an off-set relationship relative to amid-position within said air gap; means providing insulation between anyone part of said metallic foil and another part of said metallic foil;and conduction means providing electrical connection to each one of theopposite ends of said metallic foil.
 2. A transducer assembly as setforth in claim 1 wherein said strip of metallic foil is formed into acoil with successive windings displaced from superposition bypredetermined amounts which vary the inductive characteristics inpre-set manner.